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The Worst Side Effects of 5 Popular Supplements

Use caution before taking these.

More people than ever are popping supplements in hopes of improving their health, immunity or physique. But some of the most popular formulations we take to feel better can actually leave you feeling a whole lot worse, and in rare cases, can actually have dangerous effects. Here are the worst side effects of five popular supplements (all picked from ConsumerLab's 2021 list of the top 30 supplements). Read on to find out more—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Whey Protein

whey protein powder

Side effect: Diarrhea

The popular workout supplement can be difficult for some people to stomach. (Perhaps no surprise, as it's derived from milk.) Downing whey protein can lead to some uncomfortable GI effects, including gas, bloating, nausea and diarrhea. If whey's too rough on your digestive system, a plant-based protein powder might be a better option.

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Vitamin D

vitamin d in the sun

Side effect: Toxicity

Vitamin D was the #1 supplement purchased in 2020, according to ConsumerLab's data. And it's no wonder: The vitamin attracted a lot of publicity during the pandemic, starting with reports that many people with severe COVID had low levels of the vitamin. D is a very good thing for immunity, but don't go overboard. It's a fat-soluble vitamin, meaning that excess amounts aren't excreted in the urine but stored in the body. Taking too much can cause calcium to build up in your blood, a potentially serious condition called hypercalcemia. It's a rare occurrence but a good reminder to take supplements only as directed.

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Apple Cider Vinegar

Side effect: Tooth enamel loss

Apple cider vinegar is a hot supplement right now, outranking collagen and even whey protein in the ConsumerLab survey. ACV is available in capsules and gummies, but many people take the liquid formula right out of the bottle, adding it to hot water, juice, or just taking a spoonful straight-up. Experts warn against doing that too often, as ACV is highly acidic and can weaken tooth enamel, raising the risk of decay. Mixing it in water can dilute the acid, and if you take it straight, wait at least 30 minutes before brushing your teeth.

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Chia Seeds

chia seeds

Side effect: Choking

Chia seeds are high in fiber, which can improve digestion and gut health. Once ingested, the seeds expand into a thick gel. Unfortunately, if the seeds expand in your esophagus, that can cause choking and obstruct your airway. Always take chia seeds with plenty of water.

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Green Tea Extract

green tea extract

Side effect: Liver failure

In recent years, there have been several reports of liver injury and even acute liver failure linked to highly concentrated green tea extract supplements. "GTE [green tea extract] may contain solvent residues, pesticide residues, and other impurities that can cause liver damage in susceptible people," warns the United States Pharmacoepia (USP). "A specific compound in green tea that is most abundant (Epigallocatechin gallate or EGCG), can saturate the liver, increasing the potential to liver disease." If you take green tea extract, do so only as directed, and choose a brand you trust. And to get through this pandemic at your healthiest, don't miss these 35 Places You're Most Likely to Catch COVID.

Michael Martin
Michael Martin is a New York City-based writer and editor. Read more about Michael